It is imposible to say un;less we know why the email is being considered spam by the spam filter.
Here are some common causes:
1) If you are sending an HTML email, you must also create a text version. On the body tab, go to the text section and use the pencil edit icon to create a text based message.
2) some spam filters will trigger based on the from address. If the from address includes "sales" or "support" they may be treated as spam. for example: firstname.lastname@example.org